Experimental Research On Dimethyl Trisulfide And Dimethyl Sulfide Oxidation By Potassium Permanganate In Drinking Water

With the improvement of living standards,the requirements of people on water quality and safety are also improved. Due to having the city canal discharge sewage, black smelly incident broke out frequently in the urban water body;serious water pollution can cause an overgrowth of algae water and release metabolites,then cause water stink,so that the drinking water quality become poor, easy to cause customer complaint.At present,the smelling problem in drinking water has become the main reason for the people doubt the water quality at home and abroad. This topic make the dimethyl sulfide and dimethyl trisulfide as the research object,Used the method of solid-phase microextraction and gas chromatography to implement qualitative and quantitative analysis for the two kinds of material.With potassium permanganate as oxidant,we studied the efficiency of potassium permanganate oxidation of the two sub stance.The effects of four factors such as the dosage of potassium perpermanganate,initial concentration,pH and humic acid concentration on the oxidation reaction of dimethyl sulfide and dimethyl trisulfide were investigated by beaker experiments in the study Then we analyzed the reaction kinetics and the oxidation products.Used solid-phase microextraction and gas chromatography to define the qualit y and quantity of DMS and DMDS.Depart the two odor compounds with suitable programmed heating mode,Using standard to determine the retention time of DMS and DMTS,0.911 min and 5.556 min,respectively;and as a qualitative basis.Though the experiments we determined the optimum extraction condition of SPME :extraction temperature of 70 ℃,stirring speed of 500 r/min,salt concentration of 30%, gas liquid ratio of 1:2,extraction time of 35 min,then parsing 4 min,to achieve the optimal extraction effect.Under this condition,we established the standard curve of DMS and DMTS, and the linear correlation is good;At the same time,we verified the feasibility of method through the precision and recovery experiment.The results of experiments of potassium permanganate oxidation of dimethyl sulfide showed that the oxidation reaction of dimethyl sulfide under different dosage of potassium permanganate can basically complete within 10 min,the removal rate can reach 99%;and the removal rate and the reaction rate increase with the increa se of the dosage of potassium permanganate. The initial concentration of dimethyl sulfide has no effect on the removal rate and the reaction rate. The value of pH can influence the reaction rate constant,and the reaction rate constant can reach the maximum at pH =6.85.When the humic acid concentration is betw- een 0mg/L and 30mg/L,the humic acid has no effect on the removal rate of dimethyl sulfide,but has a certain inhibitory effect on the reaction rate. When the humic acid concentration is between 0mg/L a nd 15mg/L,the reaction rate constant basically keeps unchanged. When the concentration of humic acid is between 15mg/L and 20mg/L,the reaction rate constant decreases rapidly,and the reaction process becomes slowly;When the concentration of humic acid is more than 20mg/L,the reaction rate constant basically keeps unchanged. The kinetics of dimethyl sulfide decomposition by potassium permanganate in aqueous solution was found to follow the second-order rate law, the reaction rate constant is k=0.647L/(min?mg).The oxidation products of dimethyl sulfide were identified by gas chromatography–mass spectrometry and we found that dimethyl sulfide can be oxidezed to dimethyl sulfoxide.The results of experiments of potassium permanganate oxidation of dimetyl trisulfide showed that the ability of oxidation of dimethyl trisulfide under diffe rent dosage of potassium permanganate has been proved to be limited, and the oxidation time was long,for up to 2h.The removal rate and the reaction rate in crease with the increase of the dosage of potassium permanganate,but the potas sium permanganate dosage should not be too m uch, it is recommended that the best dosage is 2mg/L.The initial concentration of dimethyl trisulfide、the value of pH and the humic acid concentration in the actual water body had no effect on the oxidation reaction,but the same odor substance dimethyl sulfide ha d acer tain inhibitory effect on the oxidation reaction,the reaction process becames low ly.The kinetics of dimethyl trisulfide decom position by potassium permanganat e in aqueous solutionwas found to follow the second-order rate law,the secondorder reaction rate constant is k=0.00659L/(min?mg).Experiments showed that when the dimethyl sulfide and dimethyl trisulfide both exist in the water at the same time, the oxidation of potassium permanganate is selective,the dimethyl sulfide is more competitive, first by oxidation,also more easily by oxidation.Moreover,Compared with the theoretical curves of the two substances in the experiments and the actual response curves,it is concluded that there is a gap between the theoretical curve and the actual reaction curve,but the gap between the two curves in the whole process is not very big,so the theoretical curve can be a good guide in practice.